1. Field of the Invention
The present invention relates to a magnetic recording apparatus and a method of designing the same.
2. Description of the Related Art
With improvement in the processing speed of computers achieved in recent years, high-density recording has been required for magnetic recording apparatuses (HDD) for recording and reproducing information. However, there is a physical limit in the magnetic recording density.
In order to achieve high-density magnetic recording, it is necessary to reduce the size of magnetic domains recorded in the magnetic recording layer. For distinguishing each recorded small magnetic domain clearly, it is necessary for the domain boundaries to be smooth. For making the domain boundaries smooth, it is necessary for the magnetic particles to be small and to be separated magnetically each other. It is also necessary to decrease the thickness of the magnetic recording layer in order to reduce the magnetization transition width. Therefore, it is necessary to reduce the size of grains of a magnetic material, which are magnetically independent each other, forming the magnetic recording layer. However, if the magnetic particles are made very small, magnetic anisotropy energy, i.e., the product of magnetic anisotropy energy density Ku and magnetic particle volume, is rendered smaller than thermal fluctuation energy, with the result that it is impossible to maintain the direction of the spin once recorded. This is called a thermal fluctuation limit or a super-paramagnetic limit.
In order to avoid the thermal fluctuation, it is effective to increase the value of Ku. However, since coercive force Hc is substantially proportional to Ku, a large recording magnetic field is required for achieving a sufficient recording in such a medium. It should be noted in this connection that the characteristics of a head magnetic pole material determining the recording magnetic field have substantially reached already a physical limit, making it unreasonable to expect a further improvement in the recording magnetic field. In other words, it is impossible to comply with the demands for the increased recording density by simply increasing Ku.
Under the circumstances, proposed is a magnetic recording apparatus of a so-called “thermally-assisted magnetic recording system”, in which recording is performed by applying a magnetic field while the magnetic recording medium is being heated. Since, the magnetic recording apparatus of this type includes a heating means in addition to the construction of the conventional magnetic recording apparatus, the number of parameters for designing the apparatus is increased. It follows that tremendous work is necessary if the apparatus is designed through the large number of read/write tests of many trial manufactures of the apparatus.